Cross-reference and incorporation by reference is made to the following additional copending, commonly assigned, and commonly owned at the time of their Invention U.S. patent applications and patents: appln. Ser. No. 09/862,247 filed May 22, 2001 by Jagdish C. Tandon and Lalit (then Lingappa) K. Mestha appln. Ser. No. 09/867,042 filed May 22, 2001 by Jagdish C. Tandon, Lalit K. Mestha and Fred F. Hubble, III, now allowed appln. Ser. No. 09/535,007, filed Mar. 23, 2000, by Fred F. Hubble, III, and Joel A. Kubby, now U.S. Pat. No. 6,384,918 issued May 7, 2002 and U.S. Pat. No. 6,351,308 issued Feb. 26, 2002 from allowed appin. Ser. No. 09/448,987 filed Nov. 24, 1999 by Lalit K. Mestha.
There is provided an improvement in the color measurements of irregular surfaces, especially textiles, especially including, but not limited to, the testing and/or on-line control of color dying or other manufacturing operations for textiles. The disclosed method is especially suitable for improved yet low cost color measurements for any textiles which can change their apparent or observed color depending on the viewing or illumination angle of the area of the textile being tested. The disclosed improved color measurement system may thus be used with woven silk, polyester or other woven textiles with particular color measurement difficulties, but may also be used for color measurement of other textiles, such as carpeting and other non-woven textiles, and even threads or yarns of or for textiles.
Specifically, a desirable system for color measurements of textiles is provided that can be used easily, quickly, and uncritically in terms of the handling, positioning and orientation of the material to be tested, yet provide accurate and consistent color measurements, at relatively low cost.
Operating principles of the improved spectrophotometer color sensing architecture of disclosed embodiments herein and in the above-identified parent patent application, of which this is a CIP, have been found to provide an unexpectedly improved method of accurately measuring the colors in textiles, such as fine woven cloth, carpeting, etc., especially those with illumination or illumination reflectance angle sensitive surfaces. More accurate color measurements for these and other such unevenly light reflective surfaces can be provided by the much wider range of color target azimuthal and displacement insensitivity. Including, for example, greatly improved color measurement repeatability and reduced azimuthal variations on textured fabric samples, or fabric samples which are rotated between tests.
In some actual testing on textured fabric samples, color reflectance measurements were found repeatable with rotated fabric samples to less than 1 deltaE, using a spectrometer detector of the exemplary embodiment having a 0-45 degree illumination and detection architecture with displacement insensitive optics and six angularly disposed detectors averaging the reflected light.
The repeatability of the exemplary color measurement system output was high even for the testing of color threads. Hence the exemplary system may even be useful for knit and woven fabrics designs created from differently colored yarns. When specific colored threads are desired or required for a proposed design, the fabric designers could more accurately measure the actual thread colors in advance and be more able to accurately predict the fabric colors in advance of weaving the fabric. This type of improved workflow could reduce the production time for high quality outputs.
Also, the measured color signals of the yarn and/or fabric could be connected into a computer to appear on a display screen. This might especially help in designing fashions on a computer, by being able to import the measured colors of the textile samples. The color areas could also be moved or juxtaposed on the screen with available software. (As is well known, adjacent colors affect human color perception.)
The disclosed method of measuring color may provide cost effective improvements for various other textile/fashion retail markets, and/or graphic arts, as well as textile manufacturing operations. Other potential applications could be in carpet dyeing, coloring of fashion-ware accessories, such as knitwear and yarns, dyeing leather, color matching or control of plastic coatings, etc.
The disclosed method could be used on-line in textile manufacturing as part of direct feedback color control and correction systems, or off-line on textile samples for regular or random quality control testing. The disclosed low cost textile color measurement system can be used in numerous different color calibration or correction systems, and can be readily incorporated into the color calibration or control of various on-line color control or color processing systems.
An example of a particular long-standing commercial need is providing color matching solutions for fabric dye houses, especially for maintaining consistent colors between different xe2x80x9cdye lotsxe2x80x9d or batches. Maintaining color consistency continues to challenge even the most modern of dye houses. The properties of the supplied substrates or dyes, and the ambient processing conditions, frequently keep slightly changing. Also, color dye blends are increasingly complex. Due to such varying factors, dyers face significant challenges in producing accurate and repeatable colors, and need a better color measurement system.
The control of metamerism, where samples which appear identical under one illuminant appear different under others, is another important factor in the dye and fabric industries. The exemplary system can rapidly measure the colors of the same test target area at different wavelengths and can produce and detect different reflectance spectra therefrom that can provide for accurate broad spectral reconstruction algorithms.
In particular, the disclosed system provides improved measurement accuracy for color test surfaces which may be variously or variably tilted, curved, non-planer or otherwise varying in angular orientation relative to the color measurement system apparatus, which, in the examples herein, is an improved spectrophotometer. That is particularly desirable for enhancement of the accuracy of a non-contact spectrophotometer which can measure the colors or color densities of test surfaces spaced from the spectrophotometer, or even moving surfaces of moving color objects, webs or materials, without requiring the test surface material to be constrained against a reference surface or against the spectrophotometer. This freedom of movement of the test material, both transversely to, and variably spaced from, a spectrophotometer, is very desirable in various color measurement applications.
Further, a color measurement system allowing angular or rotational freedom of movement of the test material or media can additionally very desirably allow the color test surface thereof to have variances in angular alignment relative to a spectrophotometer. The disclosed spectrophotometer embodiment and measurement system can desirably greatly reduce measurement and output signal errors from such variances in angular alignment. Including greatly reducing measurement variances from differences in media reflectivity from media azimuthal or rotational orientation differences, such as from thread or fiber orientation differences relative to the measurement device.
As will be further described, the improved angular and azimuthal insensitivity of the embodiment herein is fully compatible with, and is shown herein combinable with, various of the spectrophotometer features of the above-cross-referenced copending commonly owned U.S. applications, especially the displacement insensitivity system, as in U.S. appln. Ser. No. 09/535,007, filed Mar. 23, 2000, by the same Fred F. Hubble, III, and Joel A. Kubby, now U.S. Pat. No. 6,384,918 issued May 7, 2002. Also it is compatible with the optional utilization multiple different photo-sites detectors such as those of the above cross-referenced Application by Jagdish C. Tendon and Lingappa K. Mestha (Ser. Nos. 09/862,247 and 09/963,042) (which are also described herein, as an alternative embodiment). An earlier patent of background interest as to colorimetry and a specific color sensor structure for color measurement of the printed sheets output of a color printer is Xerox Corp. U.S. Pat. No. 5,748,221, issued May 5, 1998 to Vittoria Castelli, et al, filed Nov. 1, 1995.
In the specific exemplary spectrophotometer embodiment further described below, it may be seen that plural different color emission LEDs sequentially project their respective illuminations substantially in parallel, perpendicularly to the color test target surface, rather than at an angle thereto, so as to provide a substantially circular, rather than elliptical, commonly illuminated area of the test target. That is, with all the LEDs centrally located together, their illumination pattern on the test target may be formed from rays that hit the target at approximately 90 degrees, i.e., normal to the target. This will produce a circular or nearly circular irradiance pattern on a selected area of the target when the target surface is at 90 degrees thereto. The photo-sensors may be optically oriented at 45 degrees to the test target to receive the reflected light from the illuminated test target. As will be further explained herein, when the test target surface deviates from said 90 degrees, this circular LED irradiance pattern becomes only slightly elliptical, with little area change, and thus causes little variance in the target irradiance and, therefore, in the signals from the photo-sensors, hence providing improved spectrophotometer angular insensitivity.
An additional feature for improved spectrophotometer accuracy in the disclosed embodiment is to provide averaging of the outputs of plural photodetectors which are angularly viewing the target irradiance area from different positions around it, on opposing sides, so as to average any varying angular and/or azimuthal reflectivity of the target area, and thus further increase the insensitivity to changes in alignment with the target area.
Although not limited thereto, the exemplary embodiments described herein may be an integral part of an automatic on-line continuous color correction system. That is because such a spectrophotometer may be affordably provided and easily mounted in the material movement or operating paths of various color dying or printing processes for non-contact (spaced) color measurements without interfering with normal movement of the media. Examples of various such color control or xe2x80x9ccolorimetryxe2x80x9d function systems are further described in the above cited co-pending applications and patents, and other art cited therein. This is in contrast to the high cost (and other unsuitability""s for on-line use) of typical laboratory spectrophotometers.
As already stated in the subject parent application xe2x80x9cit should be noted that color measurements, and/or the use of color measurements for various quality or consistency control functions, are also important for many other different technologies and applications, such as in the production of textiles, wallpaper, plastics, paint, inks, etc. Thus, the disclosed color detection system may have applications in various such other fields where these materials or objects are to be color tested.xe2x80x9d
By way of some examples of the construction or design of various other color spectrophotometer themselves, besides Xerox Corp. U.S. Pat. No. 5,748,221 above, and, the above cross-referenced U.S. appln. Ser. No. 09/535,007, filed Mar. 23, 2000 by Fred F. Hubble, III and Joel A. Kubby, now U.S. Pat. No. 6,384,918 issued May 7, 2002, there is noted HP U.S. Pat. No. 5,671,059, issued Sep. 23, 1997; and HP U.S. Pat. No. 5,272,518, issued Dec. 21, 1993; Accuracy Microsensor, Inc. U.S. Pat. Nos. 5838,451 and 5,137,364, both issued to Cornelius J. McCarthy on Nov. 17, 1998 and Aug. 11, 1992, respectively Color Savvy U.S. Pat. Nos. 6,147,761, 6,020,583, and 5,963,333; BYK-Gardner U.S. Pat. No. 5,844,680; and Colorimeter U.S. Pat. No. 6,157,454.
Of particular interest, as to the non-contact measuring of light reflectance absorption and/or transmission of test objects, including biological specimens, with a plurality of circularly arrayed angularly aimed LED""s of different wavelengths is U.S. Pat. No. 3,910,701 issued Oct. 7, 1975 to G. W. Henderson, et al.
Some patents of interest relating to densitometers include U.S. Pat. Nos. 4,553,033; 4,989,985; and 5,078,497. Patents relating to providing uniform surface irradiance include U.S. Pat. No. 5,526,190.
As used in the examples herein, unless otherwise specifically indicated, the term xe2x80x9cspectrophotometerxe2x80x9d may broadly encompass a spectrophotometer, calorimeter, and densitometer. That is, the word xe2x80x9cspectrophotometerxe2x80x9d may be given a broad definition and coverage herein. The definition or use of such above technical terms may also vary or differ among various scientists and engineers.
The following is an attempt to provide some simplified clarifications relating and distinguishing the respective terms xe2x80x9cspectrophotometer,xe2x80x9d xe2x80x9ccalorimeter,xe2x80x9d and xe2x80x9cdensitometer,xe2x80x9d and narrower definitions that may be used in some technology contexts, but not as claim limitations.
A typical xe2x80x9cspectrophotometerxe2x80x9d measures the reflectance of an illuminated object of interest over many light wavelengths, to substantially cover the humanly visible color spectra or wavelength range. A typical spectrophotometer gives color information in terms of measured reflectances or transmittances of light, at the different wavelengths of light, from the test surface. (This is to measure more closely to what the human eye would see as a combined image of a broad white light spectra image reflectance, but a spectrophotometer desirably provides distinct electrical signals corresponding to the different levels of reflected light from the respective different illumination wavelength ranges or channels.)
A xe2x80x9ccolorimeterxe2x80x9d normally has three illumination channels, red, green and blue. That is, generally, a xe2x80x9ccolorimeterxe2x80x9d provides its three (red, green and blue, or xe2x80x9cRGBxe2x80x9d) values as read by a light sensor or detector receiving reflected light from a color test surface sequentially illuminated with red, green and blue illuminators, such as three different color LEDs or three lamps with three different color filters. It may thus be considered a limited special case of a xe2x80x9cspectrophotometer,xe2x80x9d in that it provides output color information in the trichromatic quantity known as RGB.
Trichromatic quantities may be used for representing color in three coordinate space through some type of transformation. Other RGB conversions to xe2x80x9cdevice independent color spacexe2x80x9d (i.e., RGB converted to conventional L*a*b*) typically use a color conversion transformation equation, or a xe2x80x9clookup tablexe2x80x9d system, in a known manner. (Examples are provided in references cited herein, and elsewhere.)
A xe2x80x9cdensitometerxe2x80x9d typically has only a single channel, and simply measures the amplitude of light reflectivity from the test surface, such as a developed toner test patch on a photoreceptor, at a selected angle over a range of wavelengths, which may be wide or narrow. A single illumination source, such as an IR LED, a visible LED, or an incandescent lamp may be used. The output of the densitometer detector is programmed to give the optical density of the sample. A densitometer of this type is basically xe2x80x9ccolor blind.xe2x80x9d For example, a cyan test patch and magenta test patch could have the same optical densities as seen by the densitometer, but, of course, exhibit different colors.
A multiple LED reflectance spectrophotometer, as in the specific example of the embodiment herein, may be considered to belong to a special case of spectrophotometers which normally illuminate the target with narrow band or monochromatic light. Others, with wide band illumination sources, can be flashed Xenon lamp spectrophotometers, or incandescent lamp spectrophotometers. A spectrophotometer is normally programmed to give more detailed, and broader spectra, reflectance values by using more than 3 channel measurements (e.g., 4 or more channel measurements), with conversion algorithms. That is in contrast to normal three channel calorimeters, which cannot give accurate, human eye related, reflectance spectra measurements, because they have insufficient measurements for that (only three measurements).
The preferred implementations of the systems and features disclosed herein may vary depending on the situation. Also, various of the disclosed features or components may be alternatively used for such functions as gray scale balancing, turning on more than one illumination source at once.
This patent application is not related to or limited to any particular one of the various possible (see, e.g., various of the cited references) algorithms or mathematical techniques for processing the electronic signals from the spectrophotometer to generate or update color correction tables, tone reproduction curves, or other color controls, and hence they need not be further discussed herein.
Various possible color correction systems can employ the output signals of spectrophotometers, using various sophisticated feedback, correction and calibration systems, which need not be discussed in any further detail here, since the general concepts and many specific embodiments are disclosed in many other patents (including those cited herein) and publications.
A specific feature of the specific embodiment disclosed herein is to provide a method for more accurately measuring the color of irregular surface materials, including textiles which may provide dissimilar color measurements from different viewing angles, comprising illuminating a sample area of said irregular surface material approximately perpendicularly thereto and measuring the color reflected from said illuminated sample area of said irregular surface material at a substantial angle to said illuminated sample area of said irregular surface material with a plurality of separate photodetectors spaced arrayed around said illuminated sample area of said irregular surface material to receive reflected said illumination from said illuminated sample area of said irregular surface material from substantially opposing directions and at a substantial angle to said illuminated sample area of said irregular surface material.
Further specific features disclosed herein, individually or in combination, include those wherein said substantial angle is approximately 45 degrees, and/or wherein said illuminating of said sample area of said irregular surface material comprises a plurality of rapid sequential illuminations of different spectral illuminations, and wherein said irregular surface material is textile material moving relative to said plurality of separate photodetectors, and/or wherein said plurality of separate photodetectors are relatively evenly circularly positioned around said illuminated sample area of said irregular surface material, and/or wherein said plurality of separate photodetectors each comprise plural photosites with plural different spectral sensitivities, and/or wherein said irregular surface material is textile material and said textile material is carpeting, and/or wherein said irregular surface material is textile material and said textile material is woven cloth, and/or a method comprising illuminating an area of an irregular surface material substantially perpendicularly thereto and measuring the color reflected from said illuminated area of said irregular surface material at a suitable angle to said illuminated sample area of said irregular surface material with a plurality of separate photodetectors spaced arrayed around said illuminated area of said irregular surface material to receive reflected said illumination from said illuminated area of said irregular surface material from opposing directions and at a suitable angle to said illuminated area of said irregular surface material, and/or a method for accurately determining the color of a material which may provide dissimilar color measurements from different viewing angles, comprising illuminating a sample area of said surface material and measuring the color reflected from said illuminated material at an angle to said illuminated material with photodetectors situated around said illuminated material to receive reflected said illumination from said illuminated material from opposing directions and at an angle to said illuminated sample area of said material.
The disclosed system may be connected, operated and controlled by appropriate operation of conventional control systems. It is well known and preferable to program and execute various control functions and logic with software instructions for conventional or general purpose microprocessors, as taught by numerous prior patents and commercial products. Such programming or software may of course vary depending on the particular functions, software type, and microprocessor or other computer system utilized, but will be available to, or readily programmable without undue experimentation from functional descriptions, such as those provided herein, and/or prior knowledge of functions which are conventional, together with general knowledge in the software and computer arts. Alternatively, the disclosed control system or method may be implemented partially or fully in hardware, using standard logic circuits or single chip VLSI designs.
As to specific components of the subject apparatus, or alternatives therefor, it will be appreciated that, as is normally the case, some such components are known per se in other apparatus or applications which may be additionally or alternatively used herein, including those from art cited herein. All references cited or cross-referenced in this specification, including the parent application of which this is a CIP, and their references, are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be described here.